Background Vitamin D deficiency in patients with rheumatoid arthritis (RA) is commonly observed. Previous studies have investigated the relationship between vitamin D deficiency and RA and increased risk of cardiovascular events and the role of immunomodulation. While RA is recognized as a risk factor for osteoporosis, there are few reports examining the relationship between vitamin D level and bone mass or metabolism markers in RA patients compared with healthy controls.
Objectives To examine the relationship between serum 25-hydroxyvitamin D (25(OH)D) level, bone mineral density, and bone metabolic markers of RA patients compared with age-and sex-matched healthy volunteers (Vo group) using a cross-sectional method.
Methods In 2010, we began a prospective cohort study called the TOMORROW Study (UMIN000003876) which compares data from RA patients with age- and sex-matched controls (Vo) recruited through mass media. Laboratory data were collected for all participants, including 25(OH)D level, insulin resistance, bone metabolic markers (urinary pentosidine, homocysteine, collagen type 1 cross-linked N-telopeptide (NTX), and osteocalcin), and anthropometric parameters. Bone mineral density of the lower extremities and body composition were determined using whole-body dual-energy X-ray absorptiometry (DXA). The parameters were compared with healthy controls, and multiple regression analysis was carried out in the RA population only. In RA patients, disease activity score 28 was measured by clinical assessment.
Results There were 413 participants (208 RA patients, 205 Vo group; 349 females; mean age of 58 years) enrolled in the study. In RA patients (mean disease duration of 13 years), bone density was significantly lower (p<0.01; Student's t-test), and urinary NTX (p<0.01), pentosidine (p<0.01), and homocysteine (p<0.05) were higher compared with the Vo group. The serum 25(OH)D level was lower in RA patients compared with the Vo group (p<0.01) (Table). Multiple linear regression analysis in the RA population revealed no significant relationship between DXA and vitamin D level (p=0.18) or pentosidine (p=0.61).
Conclusions No relationship was found between low vitamin D level and decreased bone mass or bone quality in RA patients.
Disclosure of Interest K. Inui: None declared, T. Koike Speakers bureau: Takeda Pharmaceutical, Mitsubishi Tanabe Pharma Corporation, Chugai Pharmaceutical, Eisai, Abbott Japan, Teijin Pharma, Banyu Pharmaceutical and Ono Pharmaceutical, Y. Sugioka: None declared, T. Okano: None declared, K. Mamoto: None declared, M. Tada: None declared, H. Nakamura: None declared